1. Field of the Invention
The present invention relates to a water jacket head and, more particularly, to a water jacket head useful in the testing of compressed gas cylinders and capable of withstanding high pressure.
2. Description of the Prior Art
High pressure steel cylinders conventionally are used to contain compressed gases for a wide variety of medical and industrial uses. Literally thousands of such compressed gas cylinders are in use daily to contain under pressure oxygen, nitrogen, hydrogen, argon and other gases. To minimize the possibility of rupture of such cylinders, with the associated dangers of explosion and/or loss of combustible or poisonous gas, periodic expansion testing to determine the plastic and elastic deformation of the cylinders normally is carried out.
In accordance with U.S. Interstate Commerce Commission regulations, compressed gas cylinders used in interstate commerce must be checked once every five years by subjecting the cylinder to an internal pressure one and two-thirds times the working or rated pressure of the cylinder. Conventionally, this testing is carried out hydrostatically by placing the cylinder in a water-filled jacket connected to a burette. High pressure water is introduced into the cylinder, the pressure being raised to the requisite one and two-thirds times the nominal pressure of the cylinder. Total expansion (plastic deformation) of the cylinder then is measured by noting on the burette the amount of water displaced from the jacket as a result of the cylinder expansion.
To measure permanent expansion (plastic deformation) and percentage permanent expansion, the internal cylinder pressure is released. If the cylinder returns to its original shape, the burette will return to its zero position. If the cylinder does not return to within 10% of its original shape, as indicated by the burette reading, the cylinder is considered defective. Such a cylinder could rupture when subjected subsequently to severe shock or stress while filled with high pressure compressed gas.
To carry out such hydrostatic testing of compressed gas cylinders, it is necessary to remove the normal gas valve from the cylinder and replace it with a sealing spud through which is introduced the high pressure test water. In the past, to prevent leakage of the high pressure water between the sealing spud and the neck of the cylinder, it was necessary to tighten the spud excessively. Typically, use of a four foot wrench or a power driven torquing machine was required to achieve a sufficiently leakproof metal-to-metal seal. The resultant joint between the hardened steel spud and cylinder neck often was so tight that it was difficult to remove the spud subsequent to the test. Moreover, such wrenching was excessively time consuming.
An alternative approach of the prior art to reduce torquing was to provide a thread sealing compound between the spud and the neck. This approach was disadvantageous because the compound had some tendency to extrude and leak under the high pressure, and more important, required time for application.
Still another approach of the prior art was to utilize an O-ring seal between the neck of the cylinder and the spud. While this approach reduced the torquing requirements, it suffered various other shortcomings. First, the top of the cylinder had to be very smooth, which was seldom the case with cylinders in daily use. As a result, it often was necessary to use a power grinder to smooth the cylinder neck prior to initiation of the test. This added an extra step to the test process and was hazardous, because the grinding had to be done at shoulder height, with the ever present danger that a spark could ignite residual flammable gas in the cylinder. Moreover, the cylinder neck surfaces tended to extrude or cut the O-rings, requiring constant O-ring replacement. Further, worn threads and the high pressures to which the O-rings were subjected tended to result in leaks through the seal, voiding the test.
A further problem encountered in the prior art was how conveniently to seal the water jacket lid or head. Often complicated lid structures having multiple clamps to hold them rigidly atop the jacket were required. Such arrangements were unsatisfactory in that often they permitted air and/or water leakage from the jacket. More important, such prior art water jacket head arrangements were time consuming to connect and disconnect. In facilities where many cylinders had to be tested, the operations of attaching and sealing the spud and sealing the lid on the test jacket consumed more time than the actual expansion test itself.
These and other shortcomings of the prior art are effectively solved by the hydrostatic test head and neck seal described and claimed in U.S. Pat. No. 3,534,587, issued Oct. 20, 1970, to Carl A. Grenci and entitled "Hydrostatic Neck Seal". The hydrostatic neck seal of the Grenci patent is adapted for incorporation in a water jacket test head. The patented device permits a high pressure neck seal to be made to a gas cylinder without the necessity for using torquing machines, sealing compounds or O-rings. The water jacket head itself includes a hydrostatic seal permitting the head to be connected to the jacket rapidly and without the use of mechanical clamps. The Grenci test head thus permits significant reduction in the time required to carry out hydrostatic testing of compressed gas cylinders.
The Grenci neck seal comprises a hydrostatic chamber, the lower surface of which comprises a circular metal plate. The upper surface of the chamber comprises an extensible diaphragm of rubber or the like, the central region of which is sandwiched between a pair of rigid discs of smaller diameter than the diaphragm. A thick walled cylindrical adapter is attached coaxially to the diaphragm and discs. An elongate tube having an outer diameter less than the inner diameter of the adapter is attached coaxially within the adapter and extends downwardly through a central hole in the chamber lower plate and through an axial opening in a sealing spud depending from the lower plate. The tube is thus free to move longitudinally in response to transverse displacement of the extensible diaphragm.
An expansible grommet surrounds a portion of the tube extending beyond the spud, one side of the grommet abutting against the lower threaded end of the spud. A nut or like annular fitting is fixedly attached to the tube, adjacent the other side of the grommet. With this arrangement, when water or other fluid is introduced into the hydrostatic chamber, the resultant longitudinal motion imparted to the tube by motion of the diaphragm forces the fitting to squeeze the grommet against the end of the spud, causing the grommet to expand radially. When the spud is threadingly inserted in the neck of a compressed gas cylinder, expansion of the grommet forms a high pressure seal in the cylinder neck.
Sealing water to operate the Grenci hydrostatic neck seal may be introduced into the hydrostatic chamber via the space between the inner wall of the cylindrical adapter and the outer wall of the tube extending within the cylinder. Appropriate fluid connections are provided to permit, e.g., high pressure water required for hydrostatic expansion testing to be introduced into a compressed gas cylinder via the seal.
The water jacket test head itself comprises an upper circular metal plate spaced by means of a metal cylinder from a lower annular metal plate, the hydrostatic neck seal being attached to the latter member. A continuous rubber sleeve surrounds the metal cylinder, attached thereto by a pair of punch-locked metal bands. By introducing water or like fluid into the space between the sleeve and cylinder, the sleeve is caused to expand, e.g., against the inner wall of a cylindrical water jacket, thereby providing a hydrostatic seal.
A water jacket test head incorporating the Grenci neck seal readily may be threadingly inserted in the neck of a standard compressed gas cylinder using hand force only. When the cylinder and head then are lowered into a water jacket, water provided to the neck seal hydrostatic chamber and the region between the rubber sleeve and cylinder wall accomplishes simultaneous sealing of the head to the water jacket and high pressure sealing of the cylinder neck. Control of this sealing water may be accomplished remotely from the water jacket, as at an appropriate control console.
While the hydrostatic neck seal of the Grenci patent represents a significant improvement in the state of the art, several problems have been encountered in the use thereof. Initially, one end of the spud must be screwed tightly by wrench into the spud plate on the head. The other end of the spud is then screwed by hand into the neck of the cylinder being tested, turning the entire head, which is in turn, attached to a hoist chain, in the process. Whenever the size of the neck of the cylinder being tested changes, the spud too has to be changed. This is, invariably, a time consuming process since the head has to be removed from the hoist, taken to a vise, and the spud removed with a wrench and subsequently replaced before reattaching to the hoist. Otherwise, spare heads containing different size spuds already assembled have to be maintained in stock (with attendant costs).
In the operation of the Grenci hydrostatic test head, the longitudinal motion imparted to the tube by motion of the diaphragm causes an increasing set in the upward position of the diaphragm, resulting in eventual diaphragm failure and leakage. The entire head is welded together, making the task of servicing inside the head difficult and time consuming. In the past, welds had to be broken or awkward fishing had to be done in attempting to make mechanical repairs through the spud plate hole. Finally, the continuous rubber sleeve which surrounds the metal cylinder does not last very long and replacement is time consuming and awkward as a result of the necessary head boot clamps.